1. Technical Field
This invention relates generally to a cooling system and method for cooling a locomotive engine, and more particularly to such a cooling system for a locomotive engine having an aftercooler incorporated therewith.
2. Background Art
On Apr. 16, 1998, the Environmental Protection Agency (EPA) enacted emissions standards for newly manufactured and re-manufactured locomotive engines. Ultimately, all locomotives manufactured on or after 1973 will be required to meet the enacted emissions standards at the time of manufacture or re-manufacture. Exceptions are made to the following locomotives: electric locomotives; historic/steam powered locomotives; locomotives originally manufactured before 1973; and locomotives owned and operated by small railroads.
Three different sets of emissions standards have been adopted, with applicability of the standards dependent on the date a locomotive was first manufactured, as identified in Table 1 below. Locomotives manufactured after 1973 and not identified in the exceptions noted above, must also meet the smoke opacity limits identified in Table 2 below. Although the limits provided in Tables 1 and 2 are relatively higher than the limits provided by on-highway truck engine emission standards, it is expected that a significant reduction in NOx emissions from the status quo will result from implementation of the new standards.
TABLE 1Emission Standards for Locomotives, (g/bhp · hr)HC*CONOxPMTier 0 (1973–2001)Line-haul Duty Cycle1.05.09.50.60Switcher Duty Cycle2.18.014.00.72Tier 1 (2002–2004)Line-haul Duty Cycle0.552.27.40.45Switcher Duty Cycle1.22.511.00.54Tier 2 (2005 and later)Line-haul Duty Cycle0.31.55.50.20Switcher Duty Cycle0.62.48.10.24*HC standard is in the form of THC for diesel engines
TABLE 2Smoke Standards for Locomotives, % Opacity - NormalizedSteady-state30-sec peak3-sec peakTier 0304050Tier 1254050Tier 2204050
An important technology employed to reduce NOx emissions on turbocharged engines, such as large Diesel engines used to drive a generator on Diesel-electric locomotives, is an aftercooler. An aftercooler is a heat exchanger, typically water-to-air, that is positioned between a compressed air discharge port of the compressor stage of a turbocharger and an intake manifold of the engine, and functions to reduce the temperature of the compressed intake, or boost, air discharged from the compressor section of the turbocharger. As a result of cooling the compressed intake air in the aftercooler prior to introduction into the intake manifold of the engine, the temperature of combustion, and consequently NOx formation, are advantageously reduced.
Heretofore, all turbocharged Diesel-electric locomotives are at least jacket-water aftercooled, and their radiators sized appropriately. Therefore, the same water that passes through the engine and the engine radiator also passes through the coolant passages of the aftercooler, resulting in the need for increased radiator and cooling fan size to dissipate the additional heat load attributed to the aftercooler.
U.S. Patent Application Publication No. 2002/0174653 published Nov. 28, 2002, for a LOCOMOTIVE ENGINE COOLING SYSTEM AND METHOD by Teoman Uzkan describes a separate circuit aftercooling system, which will provide lower charge air temperatures than provided by jacket-water cooled systems. However, the system proposed by Uzkan requires increased cooling capacity to cool the separate aftercooler cooling circuit. Such an arrangement could be integrated into new locomotives, but is impractical to retrofit into existing locomotives. Existing locomotive cooling systems have insufficient cooling capability to dissipate the increased heat load imposed by an additional aftercooler.
Another cooling arrangement, also found in newer Diesel locomotive engine designs, uses a dedicated aftercooler cooling system radiator separated from the engine cooling system radiator. In this arrangement, the aftercooler cooling circuit operates independently of the cooling circuit for the engine and uses a separate coolant, i.e., the aftercooler cooling circuit is not fluidly connected to the engine cooling system, and requires a radiator and electrically-driven fan system devoted solely to cooling fluid circulating in only the aftercooler cooling circuit. For example, U.S. Pat. No. 6,006,731 granted Dec. 28, 1999 to Teoman Uzkan for a LOCOMOTIVE ENGINE COOLING SYSTEM describes a locomotive engine cooling system having separate engine and aftercooler coolant loops with separate radiators and electrically-driven fans exclusively assigned to each of the loops. Such an arrangement can be readily incorporated in the design of a new locomotive, but, because of space limitations imposed when attempting to retrofit such a cooling system to existing locomotives, cannot be considered for application to existing locomotives. As noted above, when locomotives manufactured from 1973 through 2001 are overhauled, they must meet the Tier 0 emission requirements.
The present invention is directed to overcoming the problems set forth above with respect to providing enhanced aftercooler cooling circuits for existing turbocharged locomotives. It is desirable to have an aftercooler cooling circuit that does not require modification of an existing engine coolant radiator or enlargement of the cooling fan for the engine coolant radiator. It is also desirable to have an enhanced aftercooler cooling circuit that can be readily installed in the very limited space available in the car body of existing locomotives.